1. Field of the Invention
The present invention relates to a fluid accumulator, preferably for use in connection with a hydraulic system which is to receive and deliver, respectively, large quantities of working fluid during a short period of time, comprising a housing and a piston arranged therein, which separate the working fluid, especially a liquid, from an expanding fluid, especially a gas, and which is adapted to float freely between the two phases of fluid.
2. Description of the Prior Art
The present fluid accumulator refers to the category of piston accumulators having a movable piston arranged in a housing, the one fluid normally being a liquid, for example an hydraulic oil, and the second fluid being a gas which will be compressed when liquid is pumped into the housing on the one side of the piston. When the pressure on the liquid side is reduced, the gas will expand and press the liquid or hydraulic oil out of the housing.
There are previously known fluid accumulators of this type, but such piston accumulators have been hampered with the disadvantage that the piston sealing rings which pass along the inner wall of the housing when the piston moves in pace with the pressure variations, will be apt to entrain the oil film which is deposited on the wall of the housing. This oil will mix with the gas phase of the other side of the piston, and this mixture is very unfavourable for the normal operation of the accumulator. Further, the oil will collect on the upper side of the piston and bring about, as time passes by, a sinking of the piston towards the bottom of the accumulator, resulting in a termination of the function thereof. The same effect will occur if damage on the sealing or seizing of the cylinder walls leads to leakage between the gas and the oil side of the piston.
The present fluid accumulator shall be able to store large quantities of energy, a fact which includes that it must have a large volume and be able to work under high pressure. Such a fluid accumulator is foreseen to be produced in sizes of 100 liters to 800 liters in volume. The gas filling pressure can be up to 200 bars, whereas the system pressure can be up to 350 bars, although these figures are not an upper limitation for volume and pressure.
Within this working range there are today used conventional piston accumulators, for example of the type which is disclosed in U.S. Pat. No. 2,715,419, or a battery of bladder accumulators connected in parallel.
The principle difference between a conventional piston accumulator and the present fluid accumulator is the inclusion in the conventional accumulator of a compact piston having a sealing against the cylinder wall, whereas the present accumulator comprises a free, floating piston.
It is true that other equipment working with a free, floating piston exists, inter alia some implementations of pressure surge dampers, but although these devices operate more or less according to the same principle as regards the separation of the working fluid, especially a liquid from an expanding fluid, especially a gas, these devices are not able to undertake the same working operations as the present accumulator, which comprises a piston which is designed with a view to accomplish the heavy working operations under the pressure conditions which here are relevant, i.e. in the range of 200-350 bars.
German Offenlegungsschrift No. 3.143.890, and U.S. Pat. Nos. 2,317,796, 1,959,640 and 2,725,897 all relate to a float which is formed as a sealed container. Prepared from known metallic materials these known float structures would not be able to withstand the pressure in question, and possibly would be too heavy for floating in oil.
From U.S. Pat. No. 1,116,614 there is known a flat and low floating body which presumably can be prepared from a material which can float at the pressure in question (not wood or cork). Compared with a piston such a disc-shaped flat floating body will render a poor separation of oil and gas, and it can further easily stick due to insufficient guiding. Besides, the known floating body which is arranged in a bumper, will not be able to prevent gas from seeping into the system.
From U.S. Pat. No. 1,779,448 there is known a piston which is comprised of two cylindrical parts having different diameters, the piston having an opening which is facing down towards the liquid (oil). Such a piston would be able to withstand the pressure in question, but if for example the system pressure is twice as great as the gas filling pressure, oil will be pressed up into that part of the piston which has a large diameter, and the ability of the piston or the float to separate oil and gas will then vanish.
Additionally, the apparatus according to U.S. Pat. No. 1,779,448 is arranged for absorbing surge waves in for example oil pipes and is constructed for quick inflow of oil, but without a view of enabling the oil to leave the apparatus just as quickly, as is the case in fluid accumulators. Accordingly, no preference has been included in the apparatus regarding the requirement of separating gas and liquid, as is the case in fluid accumulators.